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    <title>把新元素添加到数组的开头 - unshift()</title>
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    <h1>JavaScript 数组方法</h1>
    <h2>unshift()</h2>
    <p>unshift() 方法将新元素添加到数组的开头。</p>
    <button onclick="myFunction()">试一试</button>
    <p id="demo"></p>
    <script>
        var fruits = ["P", "A", "L", "V"];
        document.getElementById("demo").innerHTML = fruits;

        
        function myFunction() {
            fruits.unshift("L");
            document.getElementById("demo").innerHTML = fruits;
        }
    </script>
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